Genetic analysis of neurodegenerative diseases in a pathology cohort.

Molecular genetic research provides unprecedented opportunities to examine genotype-phenotype correlations underlying complex syndromes. To investigate pathogenic mutations and genotype-phenotype relationships in diverse neurodegenerative conditions, we performed a rare variant analysis of damaging mutations in autopsy-confirmed neurodegenerative cases from the Johns Hopkins Brain Resource Center (n = 1243 patients). We used NeuroChip genotyping and C9orf72 hexanucleotide repeat analysis to rapidly screen our cohort for disease-causing mutations. In total, we identified 42 individuals who carried a pathogenic mutation in LRRK2, GBA, APP, PSEN1, MAPT, GRN, C9orf72, SETX, SPAST, or CSF1R, and we provide a comprehensive description of the diverse clinicopathological features of these well-characterized cases. Our study highlights the utility of high-throughput genetic screening arrays to establish a molecular diagnosis in individuals with complex neurodegenerative syndromes, to broaden disease phenotypes and to provide insights into unexpected disease associations.

The spectrum of preclinical Alzheimer's disease pathology and its modulation by ApoE genotype.

Sporadic Alzheimer's disease (AD) usually presents clinically after 65 years of age, but its pathological changes begin decades earlier. We examined for AD pathology in the postmortem brains of 431 of subjects aged 30-65 years not clinically characterized. Among 40-49 year olds, 15% showed diffuse amyloid ß (Aß) plaques, with a prevalence of 80% in ApoE4/E4, 42% in E4/E3, and <1% in E3/E3 subjects. Aß deposits appeared after age 49 years in subjects with E3/E3 genotypes. Neuritic plaques first appeared after age 50 years and increased steadily with age in all genotypes. Insoluble Aß42 levels were highest in parietal, temporal, and frontal lobes, but barely detectable in precuneus. Tau lesions were present in the hippocampus and entorhinal cortex in 7% of subjects aged <40 years and increased steadily with age reaching near 70% in the 60- to 65-year age group. In the locus coeruleus, tau lesions were present in 72% of subjects aged 31-40 years and 94% in the 41- to 50-year age group. Both Aß and tau lesions are present in the brains of young individuals decades before the age of clinical onset of AD. Aß lesions closely correlate with the ApoE4 allele and appear as the earliest event in the development of senile plaques.

Frequency of Dermatologic Findings at Autopsy.

A complete academic autopsy includes an external examination with inspection of gross dermatologic findings. At our institution, the postmortem examination also includes a standard skin biopsy. We determined the microscopic yield of this standard postmortem skin biopsy and the overall frequency of macroscopic dermatologic diagnoses. We reviewed 389 complete autopsies conducted between 2012 and 2014. Both microscopic and macroscopic dermatologic diagnoses were analyzed. A macroscopic dermatologic diagnosis was made in 32% of cases while a microscopic diagnosis was recorded in 10% of cases. Dermatologic diagnoses were identified as leading directly to cause of death in 4% of patients and as contributing to death in another 20%. Targeted biopsies were more likely to reveal histologic abnormalities than routine biopsies from a standard anatomic site. Better training in skin gross examination in addition to systematic sampling of both skin lesions and grossly normal skin may improve diagnostic accuracy and enhance clinical pathologic correlations.

Senataxin Mutation Reveals How R-Loops Promote Transcription by Blocking DNA Methylation at Gene Promoters.

R-loops are three-stranded nucleic acid structures found abundantly and yet often viewed as by-products of transcription. Studying cells from patients with a motor neuron disease (amyotrophic lateral sclerosis 4 [ALS4]) caused by a mutation in senataxin, we uncovered how R-loops promote transcription. In ALS4 patients, the senataxin mutation depletes R-loops with a consequent effect on gene expression. With fewer R-loops in ALS4 cells, the expression of BAMBI, a negative regulator of transforming growth factor ß (TGF-ß), is reduced; that then leads to the activation of the TGF-ß pathway. We uncovered that genome-wide R-loops influence promoter methylation of over 1,200 human genes. DNA methyl-transferase 1 favors binding to double-stranded DNA over R-loops. Thus, in forming R-loops, nascent RNA blocks DNA methylation and promotes further transcription. Hence, our results show that nucleic acid structures, in addition to sequences, influence the binding and activity of regulatory proteins.

Alzheimer's disease pathology and shunt surgery outcome in normal pressure hydrocephalus.

We aimed to determine whether presence of AD neuropathology predicted cognitive, gait and balance measures in patients with idiopathic normal pressure hydrocephalus (iNPH) after shunt surgery. This is a prospective study of gait and balance measured by Timed Up and Go (TUG) and Tinetti tests, and cognitive function measured by Mini Mental Status Exam (MMSE), before and after shunt surgery in participants 65 years and older with iNPH at the Johns Hopkins University. Random effects models were used and adjusted for confounders. 88 participants were included in the analysis with a median (IQR) time of 104 (57-213) days between surgery and follow-up. 23 (25%) participants had neuritic plaques present (NP+) and were significantly older [76.4 (6.0) years], but were otherwise similar in all demographics and outcome measures, when compared to the group without neuritic plaques (NP-). NP- and NP+ participants equally improved on measures of TUG (ß = -3.27, 95% CI -6.24, -0.30, p = 0.03; ß = -2.37, 95% CI -3.90, -0.86, p = 0.02, respectively), Tinetti-total (ß = 1.95, 95% CI 1.11, 2.78, p<0.001; ß = 1.72, 95% CI 0.90, 2.53, p<0.001, respectively), -balance (ß = 0.81, 95% CI 0.23, 1.38, p = 0.006; ß = 0.87, 95% CI 0.40, 1.34, p<0.001, respectively) and -gait (ß = 1.03, 95% CI 0.61, 1.45, p<0.001; ß = 0.84, 95% CI 0.16, 1.53, p = 0.02, respectively), while neither NP- nor NP+ showed significant improvement on MMSE (ß = 0.10, 95% CI -0.27, 0.46, p = 0.61, ß = 0.41, 95% CI -0.27, 1.09, p = 0.24, respectively). In summary, 26% of participants with iNPH had coexisting AD pathology, which does not significantly influence the clinical response to shunt surgery.

Misdiagnosis of cerebellar hemorrhage - features of 'pseudo-gastroenteritis' clinical presentations to the ED and primary care.

BACKGROUND: Early-stage cerebellar hemorrhage can present with nausea or vomiting absent other neurological symptoms or signs, potentially leading to an incorrect diagnosis of gastroenteritis. We sought to determine the frequency of gastroenteritis-like presentations and delayed or missed diagnoses among patients with spontaneous cerebellar hemorrhage. METHODS: This is a retrospective, case-control analysis of atraumatic, primary cerebellar hemorrhages derived from a systematic search of surgical pathology and autopsy databases at two large urban, academic medical centers from 1984 to 2006. Hospital visit and clinical symptom data were abstracted from electronic and paper medical records for included patients. Delayed or missed diagnoses were defined as those at least one previous visit for relevant clinical symptoms in the 7 days prior to the correct diagnosis being confirmed. RESULTS: Among 254 records captured by our search filter, we identified 35 cases of pathologically proven primary cerebellar hemorrhage. Four patients (11%) were misdiagnosed initially - three with "gastroenteritis" and one with "hypertension". In this small sample, misdiagnosed patients presented more often with normal mental state (100% vs. 35%, p=0.07) and nausea/vomiting (100% vs. 58%, p=0.22). Although patients deteriorated clinically after the initial misdiagnosis, and potentially dangerous diagnostic tests and treatment strategies were instituted as a result of misdiagnosis, none of the misdiagnosed patients died or suffered major permanent harms due to diagnostic delay. CONCLUSIONS: Our study is limited by the small number of identified cases. Nevertheless, it appears that patients with cerebellar hemorrhages can present with relatively unimpressive clinical findings without obvious neurological manifestations. Such individuals are sometimes misdiagnosed with gastroenteritis or other benign disorders initially, possibly when neurologic examination, particularly gait testing, is omitted or abridged. A careful search for subtle cerebellar signs, including dysarthria, limb ataxia, nystagmus or tandem gait instability, absent in true gastroenteritis cases, could potentially reduce misdiagnosis.

A Novel Experimental Animal Model of Adult Chronic Hydrocephalus.

BACKGROUND: The pathogenesis of adult chronic hydrocephalus is not fully understood, and the temporal relationship between development of the radiological changes and neurological deterioration is unknown. OBJECTIVE: To clarify the progression of radiological-histological changes and subsequent clinical manifestations of adult chronic hydrocephalus. METHODS: Kaolin was injected bilaterally into the subarachnoid space overlying the cranial convexities in 20 adult rats. Magnetic resonance imaging (MRI) was obtained by using an 11.7 T scanner at 14, 60, 90, and 120 days after kaolin injection. Locomotor, gait, and cognitive evaluations were performed independently. Kaolin distribution and the associated inflammatory and fibrotic responses were histologically analyzed. RESULTS: Evans index of ventriculomegaly showed significant progressive growth in ventricular size over all time points examined. The greatest enlargement occurred within the first 2 months. Evans index also correlated with the extent of kaolin distribution by MRI and by pathological examination at all time points. First gait changes occurred at 69 days, anxiety at 80, cognitive impairment at 81, and locomotor difficulties after 120 days. Only locomotor deterioration was associated with Evans index or the radiological evaluation of kaolin extension. Inflammatory/fibrotic response was histologically confirmed over the cranial convexities in all rats, and its extension was associated with ventricular size and with the rate of ventricular enlargement. CONCLUSION: Kaolin injected into the subarachnoid space over the cerebral hemispheres of adult rats produces an inflammatory/fibrotic response leading in a slow-onset communicating hydrocephalus that is initially asymptomatic. Increased ventricular size eventually leads to gait, memory, and locomotor impairment closely resembling the course of human adult chronic hydrocephalus. ABBREVIATION: NPH, normal pressure hydrocephalus.

Clinical Inferences of Cardiovascular Implantable Electronic Device Analysis at Autopsy.

BACKGROUND: Cardiovascular implantable electronic device (CIED) removal and interrogation are recommended at autopsy in suspected cases of sudden cardiac death, but data on the role of nonselective post-mortem CIED (pacemaker or defibrillator) analysis in this setting are lacking. OBJECTIVES: This study undertook an institutional registry analysis to determine the utility of systematic routine CIED removal, interrogation, and analysis at autopsy. METHODS: From May 19, 2009, to May 18, 2015, autopsy subjects with a CIED at a Johns Hopkins University medical institution (Baltimore, Maryland) underwent CIED removal and interrogation by an electrophysiologist for clinical alerts. The CIED was then submitted for technical analysis by the manufacturer. The CIED interrogation, the manufacturer's technical analysis, and the final autopsy report were all cataloged in the Johns Hopkins Post-mortem CIED Registry. RESULTS: A total of 2,025 autopsies were performed; 84 subjects had CIEDs removed and analyzed. These devices included 37 pacemakers and 47 defibrillators. Overall, 43 subjects had died suddenly, and 41 had not died suddenly. Significant clinical alerts (sustained tachyarrhythmias or an elevated fluid index value) were seen in 62.8% cases of sudden deaths. In the nonsudden death cohort, 19.5% displayed a significant clinical alert. Significant association of CIED alerts were noted when comparing sudden deaths versus nonsudden deaths (p < 0.001), defibrillators versus pacemakers (p < 0.005), and cardiac versus noncardiac causes of death (p < 0.001). Manufacturer analyses revealed a case of premature pacemaker battery depletion, as well as a hard reset in a defibrillator as a result of cold exposure. CONCLUSIONS: Post-mortem CIED analysis was clinically useful in assisting with determination of the timing, mechanism, and cause of death in the majority of sudden deaths and in almost 20% of nonsudden deaths. The authors advocate CIED removal with analysis as an important diagnostic tool in all autopsies and to assist manufacturers in identifying potentially fatal device failures.

From suspected Creutzfeldt-Jakob disease to confirmed histoplasma meningitis.

A 77-year-old man with chronic obstructive lung disease who was on steroids, presented to the hospital after a fall with subacute headaches and ataxia. During the patient's hospital course, his clinical condition deteriorated with myoclonic jerks, fevers and severe encephalopathy. An extensive workup, including EEG, brain MRI and lumbar puncture, revealed possible Creutzfeldt-Jakob disease. Unfortunately, the patient failed to improve and died 12 days after admission. A brain-only autopsy revealed he had acute histoplasma meningitis with patchy superficial cerebritis.

Next-generation sequencing reveals substantial genetic contribution to dementia with Lewy bodies.

Dementia with Lewy bodies (DLB) is the second most common neurodegenerative dementia after Alzheimer's disease. Although an increasing number of genetic factors have been connected to this debilitating condition, the proportion of cases that can be attributed to distinct genetic defects is unknown. To provide a comprehensive analysis of the frequency and spectrum of pathogenic missense mutations and coding risk variants in nine genes previously implicated in DLB, we performed exome sequencing in 111 pathologically confirmed DLB patients. All patients were Caucasian individuals from North America. Allele frequencies of identified missense mutations were compared to 222 control exomes. Remarkably, ~25% of cases were found to carry a pathogenic mutation or risk variant in APP, GBA or PSEN1, highlighting that genetic defects play a central role in the pathogenesis of this common neurodegenerative disorder. In total, 13% of our cohort carried a pathogenic mutation in GBA, 10% of cases carried a risk variant or mutation in PSEN1, and 2% were found to carry an APP mutation. The APOE ε4 risk allele was significantly overrepresented in DLB patients (p-value <0.001). Our results conclusively show that mutations in GBA, PSEN1, and APP are common in DLB and consideration should be given to offer genetic testing to patients diagnosed with Lewy body dementia.

Cardiovascular implantable electronic device function and longevity at autopsy: an underestimated resource.

BACKGROUND: The feasibility and safety of postmortem cardiovascular implantable electronic device (CIED; pacemaker or defibrillator) retrieval for reuse has been shown. To date, studies indicate a low yield of reusable postmortem CIEDs (17%-30%). OBJECTIVE: The purpose of this study was to test the hypothesis that a higher rate of reusable CIEDs would be identified upon postmortem retrieval when an institutional protocol for systematic and routine acquisition, interrogation, reprogramming, and manufacturer analysis was used. METHODS: Over a 6-year period, all subjects referred for autopsy underwent concomitant CIED pulse generator retrieval and enrollment in the Johns Hopkins Post-Mortem CIED Registry. CIEDs were interrogated, reprogrammed, and submitted for manufacturer analysis. RESULTS: In total, 84 autopsies had CIEDs (37 pacemakers, 47 implantable cardioverter-defibrillators). CIEDs were implanted 2.84 ± 2.32 years before death, with 30% implanted <1 year before death. Overall, CIED postmortem longevity was 4.79 ± 3.41 years, with 56% demonstrating longevity ≥4 years (this group had an estimated mean longevity of 7.37 ± 2.44 years). Manufacturer analyses uncovered 2 falsely triggered elective replacement indication alerts, confirmed 5 correctly triggered elective replacement indication alerts, identified a recalled pacemaker, and verified that a defibrillator had undergone nonprogrammable hard reset. CONCLUSION: When a protocol for systematic and routine postmortem CIED retrieval, interrogation, reprogramming, and analysis was used, we noted that >60% of pacemakers and >50% of defibrillators demonstrated normal functional status with projected longevities >7 years on average. Formation of a national hospital-based "CIED donor network" would facilitate larger scale charitable efforts in underserved countries.

C9orf72 Hexanucleotide Repeat Analysis in Cases with Pathologically Confirmed Dementia with Lewy Bodies.

BACKGROUND: Dementia with Lewy bodies (DLB) is the second most common neurodegenerative dementia affecting the elderly. The GGGGCC hexanucleotide expansion mutation at the C9orf72 locus has been identified as a major cause of amyotrophic lateral sclerosis and frontotemporal dementia, raising the question of whether this mutation is a factor in DLB. Furthermore, a small number of clinically diagnosed DLB patients have previously been reported to carry the pathologic C9orf72 hexanucleotide repeat expansion. OBJECTIVE: To explore whether the C9orf72 mutation is present in pathologically confirmed DLB patients. METHODS: We screened a cohort of 111 definite DLB cases with extensive Lewy body pathology for the C9orf72 hexanucleotide repeat expansion using the repeat-primed polymerase chain reaction assay. RESULTS: No pathogenic expansions of the C9orf72 hexanucleotide repeat were found, suggesting that there is no causal relationship between C9orf72 and DLB. CONCLUSION: Our data illustrate that C9orf72 screening of clinically diagnosed DLB patients should only be considered in cases with a family history of motor neuron disease or frontotemporal dementia to distinguish between mimic diseases.

Alzheimer Lesions in the Autopsied Brains of People 30 to 50 Years of Age.

OBJECTIVE: To test the hypothesis that asymptomatic Alzheimer disease lesions may appear before 50 years of age. BACKGROUND: Alzheimer disease has an asymptomatic stage during which people are cognitively intact despite having substantial pathologic changes in the brain. While this asymptomatic stage is common in older people, how early in life it may develop has been unknown. METHODS: We microscopically examined the postmortem brains of 154 people aged 30 to 39 years (n=59) and 40 to 50 years (n=95) for specific Alzheimer lesions: beta-amyloid plaques, neurofibrillary tangles, and tau-positive neurites. We genotyped DNA samples for the apolipoprotein E gene (APOE). RESULTS: We found beta-amyloid lesions in 13 brains, all of them from people aged 40 to 49 with no history of dementia. These plaques were of the diffuse type only and appeared throughout the neocortex. Among these 13 brains, five had very subtle tau lesions in the entorhinal cortex and/or hippocampus. All individuals with beta-amyloid deposits carried one or two APOE4 alleles. Among the individuals aged 40 to 50 with genotype APOE3/4, 10 (36%) had beta-amyloid deposits but 18 (64%) had none. CONCLUSIONS: Our study demonstrates that beta-amyloid deposits in the cerebral cortex appear as early as 40 years of age in APOE4 carriers, suggesting that these lesions may constitute a very early stage of Alzheimer disease. Future preventive and therapeutic measures for this disease may have to be stratified by risk factors like APOE genotype and may need to target people in their 40s or even earlier.

Cardiovascular pathologies in mucopolysaccharidosis type VII (Sly Syndrome).

We present the cardiac findings from the autopsy of a 28-year-old male with mucopolysaccharidosis VII (MPS VII), also known as Sly Syndrome, whose diagnosis was confirmed by biochemical testing. The patient died a sudden cardiac death. Autopsy showed thickened and stenotic aortic valve leaflets as well as marked concentric intimal thickening of the aorta and muscular arteries. There was left ventricular hypertrophy as well as mild papillary muscle thickening and fusion. Increased colloid iron staining was seen in the small- and medium-sized arteries of the heart and at the intercalated discs. We discuss the patient's premortem echocardiographic and electrocardiographic studies. In addition, we discuss the pathogenesis of MPS VII and review previous literature on its anatomic and pathologic features.

Hypoxic-ischemic encephalopathy mimicking acute necrotizing encephalopathy.

BACKGROUND: Acute necrotizing encephalopathy is a rare childhood syndrome associated with distinct and unifying neuroimaging features that are often used for the diagnosis of this entity. PATIENT: We describe a previously healthy 9-month-old girl who presented with upper respiratory symptoms, suspected seizures, and positive nasopharyngeal rapid antigen test for influenza A virus. Magnetic resonance imaging revealed signal abnormality in both thalami, bilateral caudate nuclei, brainstem tegmentum, subcortical white matter, and cerebellar hemispheres, suggestive of acute necrotizing encephalopathy. She subsequently had a cardiac arrest, was placed on extracorporeal membrane oxygenation, and treated with methylprednisone, intravenous immunoglobulin, and plasmapheresis without apparent clinical response. On autopsy, neuropathology showed evidence of hypoxic-ischemic injury but lacked evidence of hemorrhagic necrosis, which is typically associated with acute necrotizing encephalopathy. CONCLUSION: Combined clinical and neuroimaging features may be suggestive but not sufficient for the diagnosis of acute necrotizing encephalopathy.

Initial diagnoses of patients ultimately diagnosed with prion disease.

BACKGROUND: Prion diseases are rapidly progressive neurodegenerative diseases that frequently mimic other forms of dementia making them difficult to diagnose. OBJECTIVE: To explore factors associated with the initial diagnoses of cases later determined to be caused by prion disease in an attempt to recognize key clinical variables that impact the timely diagnosis of prion disease. METHODS: A retrospective chart review performed at Johns Hopkins Medicine and the Department of Veterans Affairs Health Care System (1995-2008) was conducted. Ninety-two subjects with definite or probable prion disease were included in the analyses. Demographic, clinical, diagnostic test results, neuropathologic, molecular, and genetic data were collected using a standardized instrument and compared between initial diagnosis groups. RESULTS: Cases were separated into five broad categories pertaining to their initial diagnoses: prion disease, non-prion-related dementia, psychiatric disorder, stroke, and other. The majority of cases did not receive an initial diagnosis of prion disease (n = 76, 83%). The plurality of subjects received an initial diagnosis of a non-prion disease related dementia (n = 33, 36%). Mean survival times varied between initial diagnosis groups (p = 0.042). Times to cerebrospinal fluid 14-3-3 analysis and electroencephalogram also differed between initial diagnosis groups. CONCLUSIONS: Most patients with prion disease are initially diagnosed with a non-prion disease related dementia. Several clinical features were associated with initial diagnoses including survival time, onset of specific symptoms, and times to 14-3-3 analyses and electroencephalogram. Expanding our knowledge of the various clinical presentations of prion disease, especially dementia, may aid in the earlier diagnoses of these rapidly progressive diseases.

Hippocampal sclerosis dementia with the C9ORF72 hexanucleotide repeat expansion.

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are the main syndromes of the chromosome 9 ORF72 (C9ORF72) hexanucleotide repeat expansion, but studies have shown a substantial phenotypic diversity that includes psychiatric presentations. This study describes hippocampal sclerosis dementia (HSD) in carriers of the C9ORF72 mutation. We compared clinical and neuropathological features of HSD in carriers and noncarriers autopsied at Johns Hopkins. Carriers presented with amnesia, agitation, dissocial behavior, and impaired self-care, whereas noncarriers showed little agitation. The groups were not dissimilar in cognitive or motor dysfunction. Neuropathological examination of carriers showed cerebellar neuronal inclusions positive for ubiquitin, p62, and ubiquilin-2, and negative for TAR DNA-binding protein 43. Noncarriers did not have cerebellar inclusions. C9ORF72 repeat-associated non-ATG translation was confirmed by immunohistochemistry. These observations broaden the C9ORF72 phenotype and place HSD in the FTD spectrum. The amnesic phenotype of HSD, which is consistent with the focal hippocampal atrophy, should be included in clinical categorizations of FTD.

Mild cognitive impairment and asymptomatic Alzheimer disease subjects: equivalent ß-amyloid and tau loads with divergent cognitive outcomes.

Older adults with intact cognition before death and substantial Alzheimer disease (AD) lesions at autopsy have been termed "asymptomatic AD subjects" (ASYMAD). We previously reported hypertrophy of neuronal cell bodies, nuclei, and nucleoli in the CA1 of the hippocampus (CA1), anterior cingulate gyrus, posterior cingulate gyrus, and primary visual cortex of ASYMAD versus age-matched Control and mild cognitive impairment (MCI) subjects. However, it was unclear whether the neuronal hypertrophy could be attributed to differences in the severity of AD pathology. Here, we performed quantitative analyses of the severity of ß-amyloid (Aß) and phosphorylated tau (tau) loads in the brains of ASYMAD, Control, MCI, and AD subjects (n = 15 per group) from the Baltimore Longitudinal Study of Aging. Tissue sections from CA1, anterior cingulate gyrus, posterior cingulate gyrus, and primary visual cortex were immunostained for Aß and tau; the respective loads were assessed using unbiased stereology by measuring the fractional areas of immunoreactivity for each protein in each region. The ASYMAD and MCI groups did not differ in Aß and tau loads. These data confirm that ASYMAD and MCI subjects have comparable loads of insoluble Aß and tau in regions vulnerable to AD pathology despite divergent cognitive outcomes. These findings imply that cognitive impairment in AD may be caused or modulated by factors other than insoluble forms of Aß and tau.

Dorsolumbosacral agenesis, nonterminal myelocystocele and secondary tonsillar herniation: prenatal and postnatal MRI evaluation and pathological correlation.

We present a complex case of dorsolumbosacral agenesis associated with a nonterminal myelocystocele and secondary tonsillar herniation. The secondary tonsillar herniation, mimicking a Chiari I malformation, was evident at postnatal life with concomitant enlargement of the myelocystocele. Prenatal and postnatal MRI proved invaluable in recognizing temporal change in the position of the cerebellar tonsils. Postmortem examination confirmed the presence of a nonterminal myelocystocele and dorsolumbosacral agenesis.